<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    *{
        padding: 0;
        margin: 0;
    }
    .clearfix:after,
    .clearfix:before {
        content: "";
        display: table;
        clear: both;
    }
    .fl {
        float: left;
    }


    #header,#footer{
        width: 100%;
        background: #333;
    }
#content{
    width: 100%;
    height: 200px;

}
.left,.center,.right{
    height: 200px;
}
.left{
    width: 200px;
    background: tomato;
}
.right{
   width: 200px;
   background: turquoise;
}
.center{
    width:calc(100% - 400px);
    background: violet;
}
</style>
<body>
    <header id="header">header</header>
    <section id="content" class="clearfix">
        <div class="left fl">left</div>
        <div class="center fl">center</div>
        <div class="right fl">right</div>
    </section>
    <footer id="footer">footer</footer>
</body>
</html>